You could separate the declaration and the binding into two separate statements:

```javascript
    function recipientsChanged() {
      // update composer header whenever recipients change
      this.updateComposerHeader();
      // check for enable send whenever recipients change
      this.enableSend();
      // Clean search result after recipient count change.
      this.container.textContent = '';
    }
    recipientsChanged = recipientsChanged.bind(this);
```

...although I think this is actually *less* readable than what you have here.